The present invention relates to a method of manufacturing a radial tire having a belt (breaker) and a band wound thereon, more particularly to a method of forming a tread ring separately from a tire main body, and also relates to a tread ring forming apparatus.
In general, high speed radial tires for passenger cars, sport cars and the like are provided with a belt (breaker) As the belt cord angle is relatively large with respect to the circumferential direction, the hoop effect is less and the belt is liable to be lifted by high speed rotation. Thus, a band whose cord angle is substantially zero is further wound on the belt to provide a tight hoop effect.
On the other hand, the tire tread is usually provided with a camber. Therefore, it is preferable that the belt is also provided with a similar camber.
Such a belt camber can be obtained by a profiled belt drum of which profile is a convex line in a cross section including the drum axis and also a convex line in a cross section normal to the drum axis. Namely, the drum has a three-dimensional curvature. Such a drum is disclosed in Japanese patent publication Nos. JP-B2-5-44914 and JP-B2-6-51368. In practice, however, due to high cost, it is difficult to prepare or make such a profiled belt drum for various tire sizes. Further, it is almost impossible to exactly adjust or control the three-dimensional curvature according to the output.
Therefore, sometimes the belt camber is decreased to almost zero, though the tread camber is maintained. As a result, in the vulcanizing mold, the tread rubber is liable to be moved and compressed unevenly especially in the tire shoulder portion to disturb the uniformity of the tire.
Further, the radially inward compressive force that the belt and band receive from the inside of the mold is relatively large in the belt edge portions than the center due to the curvature corresponding to the tread camber. As a result, the band tension decreases in the tire shoulder and the high speed durability decreases.